1. Field of the Invention
The invention generally relates to microwave power dividers and combiners. In particular, the present invention relates to a reduced size 2-way power divider/combiner incorporating a low pass filter structure.
2. Background of the Invention
In a microwave system, a power divider receives a radio frequency (RF) signal or a microwave frequency signal on an input port and equally divides the power among two or more output ports. A desired impedance is maintained at the input port and at each of the two or more output ports.
FIG. 1 illustrates a conventional two-way power divider 10, commonly known as the Wilkinson power divider. Power divider 10 receives a RF signal or a microwave signal at an input port 12. The received signal is equally distributed among transmission line transformers 14 and 15 and outputted on output ports 17 and 18. The impedance, Z1, at each of input port 12 and output ports 17 and 18 is set to a value of 50 ohms, for example. The impedance, Z2, of each of transformers 14 and 15 is given by: EQU Z2=.sqroot.Z1.times.2Z1.
Thus, the impedance Z2 of each of transformers 14 and 15 is 70.7 ohms. Transformers 14 and 15 are each a quarter-wavelength transformer. The length of transformers 14 and 15 is set to be a quarter-wavelength (.lambda./4) or an odd integer multiple of .lambda./4, where the wavelength .lambda. is related to the operation frequency of power divider 10. A termination resistor or isolation resistor 16 is coupled between output ports 17 and 18.
Power divider 10 can also function as a power combiner. When incident microwave signals or RF signals are presented at output ports 17 and 18, the signals feed through transformers 14 and 15 and are combined at input port 12.
Conventional power dividers such as the Wilkinson power divider illustrated in FIG. 1 have several disadvantages. One disadvantage is that conventional power dividers have no frequency rejection property. In some microwave applications, there is a need to filter out high frequency harmonics. For instance, when an oscillator is driving a microwave transmission at 2 GHz, the 2 GHz signal includes undesirable high frequency harmonics at 6 GHz, 8 GHz, and 10 GHz which need to be filtered out for proper circuit operation.
In conventional microwave circuits, a low pass filter is connected in series with the power divider to perform a low pass filtering function of the output signal. However, the series combination of a power divider and a low pass filter greatly increases the size of the microwave circuit. Due to increasing circuit density and complexity, there is a need to reduce the component sizes of microwave circuits. Therefore, the series combination of a power divider and a low pass filter is undesirable for most microwave circuit applications because of component size consideration.
Therefore, there is a need to provide a power divider having low pass filtering capability which is also reduced in size.